IB/mlx4: Don't allocate range of steerable UD QPs for Ethernet-only device

When the device has only Ethernet ports, don't try to allocate range
of steerable UD QPs since they aren't needed.  This fixes an issue
where mlx4 VFs tried to allocate a range of UD steerable QPs, but
failed to do so.

Fixes: c1c98501 ("IB/mlx4: Add support for steerable IB UD QPs")
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>